Battery packs formed with a number of series-connected battery cells are widely employed for power supply, especially in mobile appliances. As known, in (hybrid) electric vehicles, a battery pack is used to generate a high voltage to drive the motor. In such a battery pack, the number of battery cells are coupled in series by electrically conducting power bars, wherein each power bar can electrically couple a positive electrode of one battery cell to a negative electrode of an adjacent battery cell, e.g., by soldering or bolting.
Each component on a current path in the battery pack is preferably designed to have a small resistance in order to reduce useless power dissipation, especially when a current flowing through the battery cells is large (e.g., several 100 A). Usually, the contact resistance between the power bars and the battery electrodes may be taken into account. Moreover, this contact resistance will rise if the contact gets corroded, loose, aging, etc. If the pack current is high, even a contact resistance of just 1 m would be unacceptable. For example, with a pack current of 100 A, it would give rise to a power dissipation of 10 W, which is undesirable. Furthermore, a high contact resistance would lead to a hotspot that can severely limit the lifetime of the battery cell involved. In case of severe corrosion, the temperature rise may even cause a fire or explosion.
Accordingly, it is desirable for methods and systems for contact detection in battery packs.